1. Field of the Invention
The present invention relates to a reversible thermotropic plastics molding compound, to a method for its manufacture and to its utilization. Plastics molding compounds of this kind are needed for shading systems for regulating the amount of light and the temperature. They can be used in particular for the glazing of buildings, greenhouses, cars, solar collecting systems and the like.
2. Description of the Prior Art
According to prior art, the following systems are used for thermotropic glazing of this kind. From DE 19 719 224 A1, WO 9725358 A1 and WO 9725357 A1 it is known that thermotropic gels are introduced between two sheets of glass, the thermotropic gels separating with increasing temperature, forming thus scattering centers and thus reducing the light transmission. As they cool, the thermotropic gels mix with one another again and the scattering centers disappear, as a result of which the transmission increases again. What is disadvantageous about this system is the fact that the diffusion processes occurring in the hydrogel during the separation and mixing are slow, such that only low transition times can be achieved. Furthermore, hydrogels of this kind cannot be processed thermoplastically and themselves have none of the usual functional properties for plastics.
Furthermore liquid crystals embedded in polymers are known from Solar Energie Mater. Sol. Cells (1993) volume 31, pages 197 to 214. In a similar manner, in Proc. SPIE. Int. Soc, Opt. Eng. (1992) volume 1728, pages 261 to 271, films are described which have been manufactured from liquid crystals of this type embedded in polymer. In this case, the desired thermotropic effect is based on an alteration in the structure of the liquid-crystalline phase at a corresponding temperature. Since the molecular re-arrangement of the liquid-crystalline phase is hindered with increasing viscosity of the environment, those systems also have long transition times. Furthermore, liquid-crystalline polymers of this kind are expensive materials with complex structures, which are difficult to process and which have a negative influence on the mechanical properties of the matrix polymer.
From DE 38 31 873 A1 are known mixtures of thermotropic liquid-crystalline polymers, polycarbonate and polyester. The disadvantage of these mixtures consists in the fact that the liquid-crystalline polymers, as a result of the rigid anisotropic segments, are hard and brittle, and thus have a negative effect on the toughness of glass manufactured from same.